The invention refers to an apparatus for separating contaminants from a stream of bulk material, and in particular to a separator of the deflection type having a displacement body with cone-shaped tip.
A conventional separator of this type has a first upright pipe section which concentrically encloses the displacement body to define with the latter a first annular space. A second annular space is defined between the first pipe section and a second pipe section which encloses the first pipe section and extends beyond the lower end of the first pipe section for connection with a container in which screened bulk material is collected. The container is provided with an inlet opening for sifting air which passes upwards countercurrently to the descending bulk material introduced at the to of the first pipe section, so as to force lighter components contained in the stream of bulk material through the outer annular space and to exit through an outlet conduit in the upper area of the second pipe section.
Such a separator is especially suitable for removing dust particles and other contaminants of granular bulk material. After flowing through the separator, the residual dust content of the bulk material can be 30 ppm or less.
A major part of dust particles screened in the separator is created as abrasion from the granular material during the preceding pneumatic transport. In certain types of bulk material, the pneumatic transport produces not only dusty abrasions but also other contaminants such as so-called angel hair, i.e. strand-like or hair-like components. Angel hair has a large surface compared to its mass and a substantially smaller settling velocity than granular material. Thus, it may be assumed that angel hair can fairly easily be separated. However, the opposite is true. A reason for the relatively poor degree of separation of angel hair in such conventional separators compared to the separation of dust particles is probably the large surface area of angel hair which, especially when being aligned within the separating zone at a certain angel relative to the flow direction, is struck by subsequent granular particles and forced towards the bottom.